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In-Feed Use of Heavy Metal Micronutrients in U.S. Swine Production Systems and Its Role in Persistence of Multidrug-Resistant Salmonellae

2014; American Society for Microbiology; Volume: 80; Issue: 7 Linguagem: Inglês

10.1128/aem.04283-13

1098-5336

J. J. Medardus, Bayleyegn Molla, Matthew Nicol, William M. Morrow, Päivi J. Rajala‐Schultz, Rudovick Kazwala, Wondwossen A. Gebreyes,

Chromium effects and bioremediation

ABSTRACT The study aimed to characterize the role of heavy metal micronutrients in swine feed in emergence of heavy-metal-tolerant and multidrug-resistant Salmonella organisms. We conducted a longitudinal study in 36 swine barns over a 2-year period. The feed and fecal levels of Cu 2+ and Zn 2+ were measured. Salmonella was isolated at early and late finishing. MICs of copper sulfate and zinc chloride were measured using agar dilution. Antimicrobial susceptibility was tested using the Kirby-Bauer method, and 283 isolates were serotyped. We amplified pcoA and czcD genes that encode Cu 2+ and Zn 2+ tolerance, respectively. Of the 283 isolates, 113 (48%) showed Cu 2+ tolerance at 24 mM and 164 (58%) showed Zn 2+ tolerance at 8 mM. In multivariate analysis, serotype and source of isolates were significantly associated with Cu 2+ tolerance ( P < 0.001). Fecal isolates were more likely to be Cu 2+ tolerant than those of feed origin (odds ratio [OR], 27.0; 95% confidence interval [CI], 2.8 to 250; P = 0.0042) or environmental origin (OR, 5.8), implying the significance of gastrointestinal selective pressure. Salmonella enterica serotypes Typhimurium and Heidelberg, highly significant for public health, had higher odds of having >20 mM MICs of Cu 2+ than did “other” serotypes. More than 60% of Salmonella isolates with resistance type (R-type) AmStTeKm (32 of 53) carried pcoA ; only 5% with R-type AmClStSuTe carried this gene. czcD gene carriage was significantly associated with a higher Zn 2+ MIC ( P < 0.05). The odds of having a high Zn 2+ MIC (≥8 mM) were 14.66 times higher in isolates with R-type AmClStSuTe than in those with R-type AmStTeKm ( P < 0.05). The findings demonstrate strong association between heavy metal tolerance and antimicrobial resistance, particularly among Salmonella serotypes important in public health.